In each of the disaccharides shown (a–c), (i) identify the reducing end of the sugar, (ii) tell what monosaccharides are used to make it, and (iii) tell what type of glycoside linkage is present.
(b)

검증된 단계별 안내

Identify the reducing end of the sugar: Look for the anomeric carbon that is not involved in a glycosidic bond. In the given disaccharide, the reducing end is the one with a free anomeric carbon, which is typically the hemiacetal or hemiketal group.

Determine the monosaccharides: Examine the structure to identify the two monosaccharide units. In this disaccharide, the first monosaccharide is glucose, as indicated by the presence of the six-membered ring with hydroxyl groups in the equatorial positions. The second monosaccharide is fructose, which is a five-membered ring with a ketone group.

Identify the type of glycosidic linkage: Look at the oxygen bridge connecting the two monosaccharides. The linkage is between the anomeric carbon of the first sugar and the hydroxyl group of the second sugar. In this case, it is a β(1→2) glycosidic linkage, as the oxygen bridge is formed between the first carbon of glucose and the second carbon of fructose.

Verify the orientation of the glycosidic bond: The bond is β if the oxygen bridge is above the plane of the sugar ring, and α if it is below. In this structure, the glycosidic bond is β because the oxygen is above the plane of the glucose ring.

Summarize the findings: The disaccharide consists of glucose and fructose linked by a β(1→2) glycosidic bond, with the reducing end being the free anomeric carbon on the fructose unit.

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주요 개념

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Reducing and Non-reducing Sugars

Reducing sugars are carbohydrates that can donate electrons to other molecules, typically due to the presence of a free aldehyde or ketone group. In disaccharides, the reducing end is the monosaccharide unit that retains this reactive group, allowing it to participate in redox reactions. Non-reducing sugars, on the other hand, have their reactive groups involved in glycosidic linkages, preventing them from acting as reducing agents.

Monosaccharide Composition

Disaccharides are formed by the condensation of two monosaccharides, which are the simplest form of carbohydrates. Common examples include glucose, fructose, and galactose. Understanding the specific monosaccharides that combine to form a disaccharide is crucial for identifying its properties and biological functions, as well as for determining its reducing nature.

Glycosidic Linkage

A glycosidic linkage is a covalent bond that connects two monosaccharides through a dehydration reaction, resulting in the formation of a disaccharide. The type of glycosidic linkage is defined by the specific carbon atoms involved in the bond and the orientation of the hydroxyl groups (α or β). This linkage influences the disaccharide's stability, digestibility, and overall chemical behavior.

In each of the disaccharides shown (a–c), (i) identify the reducing end of the sugar, (ii) tell what monosaccharides are used to make it, and (iii) tell what type of glycoside linkage is present.(b)